Conventional nailing tools are typically designed to be operated by actuating a trigger to control the striking of a firing-pin onto a powder charge that will propel a nail received within the barrel into a work piece. In most cases, however, the tool is used for interior decoration, where it may be necessary for a user to lift the nailing tool high enough to press it against the ceiling or an object at a distance from him/her. For this reason, shaft-operated nailing tools that have an elongated extension shaft for handling the tool by a user were developed. As illustrated in FIG. 7, one of such a shaft-operated tool includes a barrel body (80) with an annular stop (801) fastened therein. Preceding the annular stop (801) within the barrel body (80) there is a nail sheath (802), followed by a tube assemble (81) and a first spring (82) which is compressed between the tube assemble (81) and the annular stop (801).
Following the annular stop (801) within the barrel body (80) there are a positioning member (83), a sleeve (84) secured to a rear portion of the positioning member (83), a firing-pin (85) and an inner tube (86) disposed in the sleeve (84), and a connector (87) threadedly connected to the inner tube (86) for interconnecting the nailing tool and the extension shaft (870). In addition, a second spring (860) is provided in the inner tube (86) to push the firing-pin (85) forward and a third spring (861) is provided between the inner tube (86) and the positioning member (83).
In operation, when the nailing tool is pressed at the tube sheath (802) against the ceiling of the room, through the extension shaft (870) by the user, the annular stop (801) is displaced upward to the end of the tube assembly (81), against the first spring (82) between the annular stop (801) and tube assembly (81). Then, the subsequent press from the extension shaft (870) will move the connector (87) upward while compressing the second and third springs (860), (861), and eventually the firing-pin (85) is driven to strike a bullet by means of the resilience force stored in the second spring (860), once the inner tube (86) depresses a trigger member (850) projected form the periphery of the firing-pin (85) and rests against the positioning member (83).
It may be appreciated that the first, second and third springs (82), (860) and (861) are in closed relationship with each other, for example, the spring (82) must be compressed to such an extent that the tube assembly (83) is positioned in place within the barrel body (80) to contact with the annular stop (801), before the second and third springs (860) and (861) are compressed to such an extent that the inner tube (86) depress the trigger member (850).
As a result, it is necessary to calculate the elastic coefficients of the springs (82), (860) and (861) precisely. A miscalculation of the elastic coefficients of any of the springs (82), (860) and (861) will lead to a malfunction of the nailing tool, or an explosion may even occur inside the barrel body (80) itself.
From the foregoing, it is clear that the nailing tool mentioned above is possible to strike before the tube assembly (81) is positioned in place with the barrel body (80), thus result in a malfunction of the tool or even an explosion in the barrel body (80), which could be fatally harmful to the user.